This invention relates generally to radio transceiver units, and in particular, to a selective stop device for a multi-channel frequency switch.
For marketing and other reasons, manufacturers of radio communications devices typically offer several different configurations for each communications product manufactured. A particular model of mobile radio transceiver may have a "basic" or minimal configuration but may optionally be provided with additional features or "options" at additional cost.
For example, a basic transceiver configuration may provide communications over a limited number of communications channels for basic radio transmitting and receiving functions required by all users. Some users may, however, have additional requirements requiring additional features--such as additional communications channels, receiver channel scanning, etc. The ability of a manufacturer to provide such additional "options" permits increases in the flexibility, versatility, desirability and range of applications of the product without penalizing purchasers of the basic configuration with increased cost. Purchasers of the basic model pay a minimum price for the minimal configuration, while users requiring additional "option" features pay an increased price based on the number and type of options required.
In the past, additional options were generally provided by incorporating additional components and circuitry into the device. For example, in the past, channel scanning capability or additional operating channels were added by installing additional frequency selection circuitry into the transceiver. Similarly, the tone activated squelch option typically required an additional tone decoder circuit to be installed. Transceiver designers used modular architectures to accommodate additional plug-in "option modules".
An example of this design approach is the prior art "MLS" series radio transceivers manufactured for General Electric Company by Japan Radio Corp. These "MLS" transceivers include basic transceiver circuitry disposed within a housing. The front panel assembly of the transceiver housing was manufactured separately, and consists of a separable front panel "escutcheon" plate. Mechanically mounted to the escutcheon plate is a printed circuit board which plug-connects to the basic transceiver circuitry when the escutcheon plate is mechanically fastened to the housing. The escutcheon plate and associated printed circuit board comprises a module separable from the transceiver main housing and basic circuitry. The module includes user controls mounted on the escutcheon plate and circuitry required to connect user controls mounted on the plate to the transceiver circuitry.
Since different "option" features in many cases require different additional user controls, different models of escutcheon plate modules were produced for the "MLS" series transceivers. In particular, the "MLS" transceiver was made available in five different versions: (1) a two-channel "basic" version; (2) an 8-channel version with the scan feature; (3) a 16-channel version without scan; and (4) a 16-channel version with scan feature. Five different interchangeable escutcheon plates with different user control arrangements corresponding to these five different transceiver versions were also made. The particular escutcheon plate/control panel installed on a particular "MLS" transceiver limited the transceiver features the user could access. For example, the escutcheon plate corresponding to the "MLS" transceiver versions with 16-channel capability and no scan feature does not have a control to actuate the scan feature--preventing the user from obtaining the of the scan feature. Similarly, the escutcheon plates corresponding to the 8-channel transceiver versions do not include user controls to access more than 8 channels.
Since all "MLS" transceivers included identical basic transceiver circuitry and main housing, reduced manufacturing costs and increased reliability derived from large scale manufacturing were obtained. Specific purchaser selected options could be provided in a particular unit simply by installing the appropriate escutcheon plate module --a procedure which could be performed in the field if desired. Incorporation of the circuitry performing the option functions and user controls interacting with such circuitry within the same front panel escutcheon plate module permitted a transceiver to be reconfigured by simply "unplugging" one module and "plugging in" a different module (further increasing reliability and decreasing manufacturing costs).
In this regard, see commonly assigned U.S. Pat. No. 4,941,174.
In order to adapt a unit to a customer's frequency requirements, it has been the practice to modify the internal construction of the frequency selection switch by the addition of a pair of stop elements. This procedure undesirably delayed the final assembly of the unit until the customer's requirements were known.
It is a principal object of this invention to provide a selective stop device which permits a multi frequency selector switch to be easily adapted to permit any consecutive series of frequencies to be set from one through any number from one to fifteen, in a transceiver unit which otherwise has a sixteen channel capability, and which has otherwise been substantially completely assembled. In other words, the rotational movement of the switch can be limited to index only channel one; channels one and two; channels one through three, etc., up through a series including channels one through fifteen. In the event full sixteen channel capability is desired, the limit mechanism is simply removed, and the switch is utilized in its normal fashion.
In an exemplary embodiment of the invention, a generally cylindrical frequency selector knob is mounted by means of a set screw to an output shaft of a multi frequency selector switch mounted within the transceiver unit housing. To facilitate assembly and disassembly of the knob, a set screw is provided which extends radially through a bore provided in the knob for engagement with a flat surface provided on the switch shaft.
A top plate of the transceiver unit housing, through which the multi channel frequency selector switch shaft protrudes, is marked with indicia corresponding to, for example, frequencies 1-16 in a circular array about the selector knob. During assembly, the frequency selector switch shaft is rotated in a counterclockwise direction until stopped by an internal limit provided within the switch. This position corresponds to channel one. With the shaft in this position, the knob is mounted on the shaft and tightened by the set screw in an orientation such that a channel indicator on the knob points to the channel one indicia on the top plate of the housing. In this configuration, the frequency selector knob is indexable in stepwise fashion through channels one through sixteen.
As discussed hereinabove, however, the otherwise standardized construction of the unit may be configured to a different version, for example, a unit with four or eight channel capability, even though the unit is capable of a full sixteen channel range. In order to facilitate quick and simple conversion of the otherwise standardized and subsequently completely assembled unit to these different versions, a stop plate or disc is provided between the top plate of the unit housing and the lower surface of the selector knob in order to limit the rotation of the knob in a predetermined manner. Advantageously, no modification to the internal construction of the selector switch is required.
Specifically, the stop plate or disc is formed with a plurality of inwardly directed teeth on its lower surface which are adapted to mesh with a plurality of corresponding teeth formed within a recess in the top plate of the unit housing. At the same time, the upper surface of the disc or stop plate is formed with a circular recess defined by inner and outer peripheral walls, the continuity of the recess being interrupted by a radially oriented stop bar. The disc or plate is also provided with a centralized bore for slidably mounting the disc on the switch shaft as described below.
When it is determined that the transceiver unit is to have less than a sixteen channel capability, the frequency selector knob is removed and the stop plate or disc is slidably mounted on the switch shaft with the stop bar arranged to point to that channel which exceeds the desired maximum channel range by one. The meshing teeth on the underside of the disc and within the recess of the top plate thereafter prevent any rotational movement of the disc. By way of example, if a channel sequence of one through eight is desired, the disc is arranged so that the stop bar points to numeral nine on the top plate. The knob is then replaced on the shaft and tightened with the set screw such that the frequency indicator provided on the knob points to channel one. Now, the knob is rotatable in stepwise fashion consecutively from channel one through channel eight, it being understood that since the stop bar occupies a channel position, i.e., channel nine, rotation beyond the channel eight position is effectively prevented.
In a similar manner, any consecutive series of channels may be selected by the appropriate adjustment of the stop plate or disc.
It will therefore be appreciated that in one exemplary embodiment, the present invention is directed to a radio transceiver unit which includes a housing; a frequency switch mounted within the housing; and a rotatable knob for indexing the switch to a plurality of predetermined frequencies from one to n (where n=16 in a preferred embodiment), the knob having a frequency indicator thereon, and the housing having frequency indicating indicia thereon; the improvement comprising stop means interposed between the switch and the knob for selectively limiting rotation of the knob to any consecutive series of predetermined frequencies from one to n-1.
Other objects and advantages of the present invention will become apparent from the detailed description which follows.